Rare-earth metals (REM) gadolinium and dysprosium, and also the Gd–H and Dy–H systems in which magnetic order–order and order–disorder phase transitions are accompanied by significant magnetocaloric effect, have been studied. The materials have been prepared in various structural states. It is stated that there is a substantial difference of their functional properties in the dependence on the features of the structural state and also on the existence of a gas-forming impurity. It has been proved experimentally and theoretically that the Curie temperatures of Gd samples with grain sizes of ~200 nm increases as a result of hydrogenation, while the magnetic phase transition temperatures of Dy are almost unchanged Inhomogeneities.